Ceramic igniters such as those used in fuel burning devices including domestic and industrial liquid fuel and gas burning appliances are well known in the art. See, for example, U.S. Pat. Nos. 3,875,477; 3,928,910; 3,875,477 and Re. 29,853. Despite the recent interest in ceramic igniters, the conventional pilot light igniter still enjoys widespread use. The pilot light, however, is an energy wasting igniting system since it constantly burns. In fact, surveys reveal that pilot light use is responsible for over 10% of the total gas consumed in the United States yearly. Despite this disadvantage, ceramic igniters have not replaced pilot lights on a widespread basis for a number of reasons including their high cost and lack of strength and reliability.
One of the key elements that contributes to the high cost of ceramic igniters is the process used to make the igniters. While igniters exist in various shapes and configurations, the hairpin-shaped igniters are the most popular due to the design being cost effective to manufacture because of the relatively simple forming, firing and assembly techniques required. Also, when an element does fail, fractured pieces of the ceramic will generally fall away from the electric current source minimizing the likelihood of an electrical short which could damage control electronics, valves, motors, etc. in the appliance.
The process used to prepare such hairpin-shaped igniters generally comprises forming a composite of ceramic powders by pressing a mixture of powders to about 60-70% of its theoretical density to form a billet in the green state. The hot pressed billet is than sliced into pieces or tiles. The tiles are then boron nitride coated and densified. To form the desired hairpin-shape, the densified tile is then slotted using a diamond wheel. The process of slotting the tiles, when in the dense state, is costly and complex. One apparent solution to this cost and technical problem would be to pre-slot the tiles in the green state. Pre-slotting, however, has not heretofore worked since the pre-slotted hairpin igniters were found to fracture during the subsequent densification process.
Accordingly, it is an object of the present invention to develop a ceramic igniter which can be manufactured simply and at a relatively low cost while also being structurally stable.